Experimental physicists conduct research (experiments) to verify or disprove theories, and to discover new phenomena or behavior. Most theoretical advances come in response to experimental observations that are puzzling or unexplainable by existing theories.

On the other hand, engineers build devices (usually practical) using well known principles. Parts of engineering are mathematical and creative (think information theory), and some engineering can look like experimental physics (investigations into strength of materials). In other words, sometimes the lines blur. However, most engineers build things (electric toothbrushes, iPods, computers, buildings, bridges, cell phones, space shuttles) and the vast preponderance of engineering is applied.

Staff: Mentor

Theoretical physicists do advance our knowledge about universe but experimental physicists only apply the concepts of those theories, right? But, isn't this what engineers do as well?

No. Experimental physicists are still theoretical physicists. They do experiments to test theories. Depending on the area of research, a physicist may look more like a mathematician than an astronomer, but they are still just two parts of the same thing. One cannot exist without the other.

I realize, in any case, that the distinction between theoretical and experimental physics is pretty lively argument and I blurred the lines a little. Googling turns up lots of hits on that, including a previous thread of ours: https://www.physicsforums.com/showthread.php?t=74280

Gustav Dahlén received the Nobel Prize in 1912 for his invention of the automatic lighthouse (which btw is quite a clever piece of engineering AND has saved many lifes) although that was controversial even back then.
Kilby was a controversial choice, there were PLENTY of people who objected (even in Sweden). There have been several prices awarded for inventing scientific equipment (e.g. the bubble chamber) but Kilby is as far as I know the only "commercial" engineer to have received the price in recent years.
Kilby shared the price with Alferov and Kroemer and selecting them was less controversial, mainly because heterostructures has been a "hot topic" in physics for quite a while.

Slightly OT but even some physicists that work in very "theoretical" fields have degrees in engineering, e.g. Max Tegmark has a MSc in engineering (well, engineering physics).